A typical drill rig comprises a tower which supports a drill head that in turn rotates a drill string. The drill head linearly traverses up and down the tower to enable the drilling of a hole. The traversing of the drill head and drill string is effected by one or more hydraulic rams. When initially drilling the hole, the hydraulic rams are operated to provide a pull down force to the drill string in order to enable it to penetrate into the ground. As hole depth increases, the length and thus the weight of the drill string increases. Eventually the weight of the drill string will reach a point where it is necessary to apply pull back to the drill head to reduce the contact force or pressure of the drill bit on a toe of the hole. This extends drill bit life thereby reducing down time involved in tripping the string to change the bit. The maximum pull back force provided by the hydraulic rams determines the maximum depth hole that can be drilled by a particular drill rig.